Gas sensor

Abstract

A porous Al 2 O 3 thick film covers the SrTiO 3 layer of an oxygen sensor, said SrTiO 3 layer being contacted by means of two Pt electrodes and deposited on an Al 2 O 3 substrate. The electrically insulating Al 2 O 3 layer bears a protective layer, which is exposed to the exhaust gas and is preferably also made of SrTiO 3 . This construction ensures that the output signal of the sensor representing the oxygen partial pressure then depends only on the resistance or, respectively, conductivity value of the non-contaminated SrTiO 2 sensor layer.

What is claimed is: 
     
       1. A sensor for detecting at least one gas of a gas mixture, the gas to be detected having a partial pressure, the gas mixture including at least one constituent capable of damaging the sensor, the sensor comprising: a sensor element having an electrical resistance value or conductivity value dependent upon the partial pressure of the gas to be detected, the sensor element being disposed on top of a substrate, the sensor element further being connected to an electrode system, the sensor element being disposed between a porous electrically insulating layer and the substrate, the porous electrically insulating layer being disposed between the sensor element and a porous top layer comprising a material that bonds chemically with the constituent of the gas mixture that is capable of damaging the sensor element.   
     
     
       2. The sensor of claim 1 wherein the sensor element further comprises at least one gas-sensitive region, the porous electrically insulating layer covering at least the gas-sensitive region of the sensor element. 
     
     
       3. The gas sensor of claim 1 wherein the porous electrically insulating layer comprises a catalyst. 
     
     
       4. The gas sensor of claim 1 wherein the porous top layer comprises a catalyst. 
     
     
       5. The gas sensor of claim 1 wherein the porous electrically insulating layer comprises a material selected from the group consisting of Al 2  O 3 , MgO and SiO 2 . 
     
     
       6. The gas sensor of claim 1 wherein the sensor element and the porous top layer are fabricated from a same material. 
     
     
       7. The gas sensor of claim 1 wherein the sensor element comprises a semiconducting metal oxide. 
     
     
       8. The gas sensor of claim 1 wherein the sensor element comprises a metal oxide doped with a donor. 
     
     
       9. The gas sensor of claim 1 wherein the sensor element comprises a material selected from the group consisting of SrTiO 3 , BaTiO 3 , CaTiO 3 , CeO 2 , TiO 2 , Ga 2  O 3 , WO 3 ,. A/VO 4  and FeVO 4 . 
     
     
       10. The gas sensor of claim 1 wherein the porous electrically insulating layer completely covers the sensor element. 
     
     
       11. A sensor for detecting at least one gas of a gas mixture, the gas to be detected having a partial pressure, the gas mixture including at least one constituent capable of damaging the sensor, the sensor comprising: a sensor element having an electrical resistance value or conductivity value dependent upon the partial pressure of the gas to be detected, the sensor element comprising at least one gas-sensitive region and a metal oxide doped with a donor, the sensor element being disposed on top of a substrate, the sensor element further being connected to an electrode system, the sensor element being disposed between a porous electrically insulating layer and the substrate, the porous electrically insulating layer comprising a material selected from the group consisting of Al 2  O 3 , MgO and SiO 2 , the porous electrical insulating layer covering at least the gas-sensitive region of the sensor element, the porous electrically insulating layer being disposed between the sensor element and a porous top layer comprising a material that bonds chemically with a constituent of the gas mixture that is capable of damaging the sensor element.   
     
     
       12. The gas sensor of claim 11 wherein the porous electrically insulating layer comprises a catalyst. 
     
     
       13. The gas sensor of claim 11 wherein the porous top layer comprises a catalyst. 
     
     
       14. The gas sensor of claim 11 wherein the sensor element and the porous top layer are fabricated from a same material. 
     
     
       15. The gas sensor of claim 11 wherein the sensor element comprises a semiconducting metal oxide. 
     
     
       16. The gas sensor of claim 11 wherein the sensor element comprises a material selected from the group consisting of SrTiO 3 , BaTiO 3 , CaTiO 3 , CeO 2 , TiO 2 , Ga 2  O 3 , WO 3 , A/VO 4  and FeVO 4 . 
     
     
       17. The gas sensor of claim 11 wherein the porous electrically insulating layer completely covers the sensor element. 
     
     
       18. A method of measuring an oxygen partial pressure in an exhaust gas of an internal combustion engine, the method comprising the following steps: providing a sensor element having an electrical resistance value or conductivity value dependent upon the partial pressure of the gas to be detected, the sensor element being disposed on top of a substrate, the sensor element further being connected to an electrode system, the sensor element being disposed between a porous electrically insulating layer and the substrate, the porous electrically insulating layer being disposed between the sensor element and a porous top layer comprising a material that bonds chemically with the constituent of the gas mixture that is capable of damaging the sensor element,   exposing the sensor to the exhaust gas stream of the engine, measuring the resistivity or conductivity of the sensor element, calculating the oxygen partial pressure in the exhaust gas based upon the resistivity or conductivity of the sensor element.